JP2014104556A - Manufacturing method of gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a gear capable of reducing surface roughness of tooth surfaces and improving the strength of the tooth surfaces.SOLUTION: The manufacturing method of a gear includes the steps of: applying compressive residual stress on tooth surfaces of teeth, engaging with each other; and reducing the height of protrusions of the tooth surfaces on which the compressive residual stress is applied and performing a finish so as to have predetermined surface roughness. The reduction amount of the height of the protrusions of the tooth surfaces is obtained so that the height of the protrusions of the tooth surfaces, reduced by the finish so as to have the predetermined surface roughness is equal to or under oil film thickness lying between the teeth engaging with each other, and at the step of applying the compressive residual stress, the compressive residual stress is applied so that the depth where the compressive residual stress is largest is the depth obtained by adding quantity of a polish of the tooth surfaces, to a target depth where the compressive residual stress of the gear finished so as to have the predetermined surface roughness is largest.

Description

  The present invention relates to a manufacturing method of a gear that transmits torque by meshing teeth with each other, and more particularly to a manufacturing method of a gear that applies compressive residual stress to a tooth surface.

  Gears are first made into a rough shape from the raw material through turning and gear cutting. In order to suppress or prevent the occurrence of pitching, compressive residual stress is applied to the tooth surface. As a method for applying the compressive residual stress, shot peening processing, liquid honing processing, or the like in which particles are jetted onto a tooth surface is known. After applying the compressive residual stress by each of these processing methods, the gear surface is finished by reducing the surface roughness of the tooth surface by polishing or rolling.

  When the tooth surface is polished after applying compressive residual stress to the tooth surface as described above, the convex portion of the tooth surface is removed, but the depth of the concave portion (dimple) formed on the tooth surface is also reduced. As a result, the lubricating oil held on the tooth surface may be reduced. Therefore, in the gear manufacturing method described in Patent Document 1, after the tooth surface is polished, liquid honing or shot peening is performed to impart compressive residual stress, and dimples are formed on the tooth surface.

  On the other hand, when polishing is performed after shot peening or liquid honing is performed on the tooth surface, even the layer to which compressive residual stress is applied is removed by polishing, or the distance from the tooth surface to the layer to which compressive residual stress is applied is increased. There is a possibility of shortening. Therefore, the gear described in Patent Document 2 is finished by reducing the surface roughness by polishing the tooth surface other than the tooth root after applying compressive residual stress by shot peening.

  Patent Document 3 discloses that a gear having a smooth tooth surface and a plurality of dimples can reduce the surface pressure and the friction coefficient by increasing the oil film thickness. Further, in Patent Document 4, compressive residual stress can be imparted to the tooth surface of the gear to be processed by meshing and rotating the gear to be processed and the gear to be processed having a plurality of convex portions formed on the surface. A processing method that can reduce the surface roughness is also described.

JP 2009-127842 A Japanese Patent Laid-Open No. 11-207522 Japanese Unexamined Patent Publication No. 07-293668 JP 2012-179678 A

  As described in Patent Document 1 described above, when liquid honing or shot peening is performed after polishing, dimples that retain lubricating oil can be formed on the tooth surface, but the surface of the polished tooth surface The roughness becomes at least rough. For this reason, protrusions may be formed on the tooth surfaces, which may increase power loss during power transmission, or create a location where the lubricating oil does not intervene between the tooth surfaces. On the other hand, as described in Patent Document 2, if the tooth surface is polished after performing shot peening, the layer loaded with compressive residual stress is removed by shot peening, or the tooth surface and There is a possibility that the distance from the layer loaded with compressive residual stress may be shortened. Therefore, even if compressive residual stress is applied, the effect is reduced, and the pitting resistance may be lowered.

  The present invention has been made paying attention to the above technical problem, and provides a gear manufacturing method that can reduce the surface roughness of the tooth surface and improve the strength of the tooth surface. It is intended.

  In order to achieve the above object, the invention of claim 1 is characterized in that a compressive residual stress is applied to tooth surfaces of teeth that mesh with each other, and a height of a convex portion of the tooth surface to which the compressive residual stress is applied is reduced. And a step of finishing to a predetermined surface roughness, the height of the convex portion of the tooth surface reduced by finishing to the predetermined surface roughness is between the meshing teeth. In the step of obtaining the amount by which the height of the convex portion of the tooth surface is reduced so as to be equal to or less than the intervening oil film thickness, and applying the compressive residual stress, the depth at which the compressive residual stress is maximized In the manufacturing method, the compressive residual stress is applied as a depth obtained by adding an amount of polishing the tooth surface to a target depth at which the compressive residual stress in the gear finished to a surface roughness of the maximum is obtained. is there.

  A second aspect of the present invention is the gear manufacturing method according to the first aspect, wherein the oil film thickness is obtained based on an average tooth surface speed of the teeth meshing with each other.

  According to the present invention, before applying the compressive residual stress, the amount of reduction in the height of the convex portion of the tooth surface is obtained from the oil film thickness interposed between the teeth meshing with each other, and the convex portion of the tooth surface is reduced. The amount to be added is added to determine the depth at which the compressive residual stress is maximized, and the compressive residual stress is applied. Therefore, the power loss when the gear transmits power can be reduced by reducing the height of the convex portion of the tooth surface and finishing to a predetermined surface roughness. Moreover, even if the height of the convex portion of the tooth surface is reduced, the depth at which the compressive residual stress is maximized can be set as the target depth, so that the strength of the tooth surface can be improved.

  Further, since the height of the convex portion of the tooth surface is less than the oil film thickness obtained based on the average tooth surface speed of the tooth surfaces meshing with each other, the tooth surface is in direct contact when the gear transmits power. This can be suppressed or prevented. In other words, since a gear can be formed so as to transmit power by interposing an oil film between tooth surfaces, power loss when the gear transmits power can be further reduced.

It is a figure for demonstrating that the depth where compression residual stress becomes the maximum changes before and after grind | polishing a tooth surface. It is a figure which shows the surface roughness of a rough shaped material. It is a figure which shows target surface roughness.

  In the gear manufacturing method according to the present invention, a rough shaped material is produced from a raw material through processing such as turning and gear cutting, and a compressive residual stress is applied to the tooth surface of the rough shaped material. It is intended to process various gears such as spur gears and helical gears. In the gear formed in this way, it is preferable that the tooth surfaces transmit power by interposing lubricating oil in order to suppress or prevent the tooth surfaces of the gears meshing with each other from directly contacting each other. Therefore, it is finished to a predetermined surface roughness so that the height of the convex portion of the tooth surface is equal to or less than the thickness of the oil film. In addition, as a method of reducing the height of the convex part of a tooth surface, it can carry out by various methods, such as the method of grind | polishing a tooth surface or performing the rolling which presses a tooth surface.

この式で、ｈc は油膜厚さ、Ｅは歯車を形成する材料の弾性定数、ｕは平均歯面速度（＝（ｕ_１＋ｕ_２）／２）、Ｒｘは接触している楕円体の互いに直交する一方の主曲率面の半径をそれぞれＲ_ｘ１、Ｒ_ｘ２とした場合に（Ｒ_ｘ１ ^−１＋Ｒ_ｘ２ ^−１）^−１で表される値、Ｒｙは他方の主曲率面の半径をそれぞれＲ_ｙ１、Ｒ_ｙ２とした場合に（Ｒ_ｙ１ ^−１＋Ｒ_ｙ２ ^−１）^−１で表される値、η_０は大気圧でのオイル粘度、αはオイルの粘度−圧力係数であって一般的な鉱油では「２０Ｇｐａ^−１」程度である。また、ｕ_１は一方の歯車における噛み合い部の歯面速度、ｕ_２は他方の歯車における噛み合い部の歯面速度である。したがって、潤滑油の粘度や歯車の諸元は固定値であるため、平均歯面速度ｕが増大すると、油膜厚さｈc が増大し、平均歯面速度ｕが低下すると、油膜厚さｈc が低下する。そのため、車両に搭載された歯車の場合には、エンジン回転数がアイドル回転数程度となるように運転している時には、歯車の回転速度が比較的低速であり平均歯面速度ｕが小さいため、エンジン回転数がアイドル回転数程度となるように運転している時における平均歯面速度ｕに基づいて油膜厚さを求め、歯面の凸部の高さが、その油膜厚さ以下となる表面粗さを定めることが好ましい。なお、ここで定める表面粗さの指標としては、最大高さ粗さＲz や粗さ曲線の最大山高さＲq などの表面粗さを定める種々の指標とすることができる。以下の説明では、最大高さ粗さＲz を例に挙げて説明し、上記の式に基づいて定められる最大高さ粗さＲz 、すなわち研磨後の歯面の目標最大高さ粗さを、目標表面粗さＲztと記す。また、以下の説明では、最大高さ粗さを、単に表面粗さと記す。 On the other hand, the oil film thickness interposed between the tooth surfaces changes in accordance with the average tooth surface speed of the portion where the gears mesh with each other. Specifically, the oil film thickness interposed between the tooth surfaces can be obtained by the following equation.

In this equation, hc is the oil film thickness, E is the elastic constant of the material forming the gear, u is the average tooth surface speed (= (u ₁ + u ₂ ) / 2), and Rx is orthogonal to the contacted ellipsoid. When the radii of one main curvature surface are R _x1 and R _x2 , respectively, the value represented by (R _x1 ⁻¹ + R _x2 ⁻¹ ) ⁻¹ , Ry is the radius of the other main curvature surface, R _y1 , R _y2 , the value represented by (R _y1 ⁻¹ + R _y2 ⁻¹ ) ⁻¹ , η ₀ is the oil viscosity at atmospheric pressure, α is the oil viscosity-pressure coefficient, and is a general mineral oil Then, it is about “20 Gpa ⁻¹ ”. U ₁ is the tooth surface speed of the meshing portion of one gear, and u ₂ is the tooth surface speed of the meshing portion of the other gear. Therefore, since the viscosity of the lubricating oil and the specifications of the gear are fixed values, when the average tooth surface speed u increases, the oil film thickness hc increases, and when the average tooth surface speed u decreases, the oil film thickness hc decreases. To do. Therefore, in the case of a gear mounted on a vehicle, when the engine is operated so that the engine speed is about the idle speed, the rotational speed of the gear is relatively low and the average tooth surface speed u is small. Surface where the oil film thickness is obtained based on the average tooth surface speed u when the engine speed is about the idle speed and the height of the convex part of the tooth surface is equal to or less than the oil film thickness It is preferable to determine the roughness. In addition, as an index of the surface roughness determined here, various indices for determining the surface roughness such as the maximum height roughness Rz and the maximum peak height Rq of the roughness curve can be used. In the following description, the maximum height roughness Rz will be described as an example, and the maximum height roughness Rz determined based on the above formula, that is, the target maximum height roughness of the tooth surface after polishing, It is written as surface roughness Rzt. In the following description, the maximum height roughness is simply referred to as surface roughness.

この式で、Ｒpqは、ＪＩＳ Ｂ０６７１−３で規定されているとおり、プラトー領域に当てはめられた回帰直線の傾斜（ＪＩＳ Ｂ０６７１−３）であり、Ｒpq_１は互いに噛み合う歯車の一方側、Ｒpq_２は互いに噛み合う歯車の他方側の値である。そして、上式を満たす歯面の最大高さ粗さＲztや粗さ曲線の最大山高さＲq を定める。 Specifically, the target surface roughness Rzt of the tooth surface is determined so as to satisfy the following formula.

In this equation, Rpq is the slope of the regression line applied to the plateau region (JIS B0671-3) as defined in JIS B0671-3, Rpq ₁ is one side of the meshing gears, Rpq ₂ is It is the value on the other side of the gears meshing with each other. Then, the maximum height roughness Rzt of the tooth surface satisfying the above formula and the maximum peak height Rq of the roughness curve are determined.

  Therefore, the amount polished for reducing the surface roughness of the tooth surface is the difference between the surface roughness Rza of the rough profile and the target surface roughness Rzt. In other words, in order to set the surface roughness of the tooth surface to the target surface roughness Rzt, the difference between the surface roughness Rza of the rough profile and the target surface roughness Rzt, and the tooth surface are polished. FIG. 2 shows a graph (actual measurement value) when the surface roughness of the rough profile is measured, and FIG. 3 is a graph schematically showing the surface roughness after polishing the rough profile. (Target value).

  On the other hand, as a processing method for imparting compressive residual stress to the tooth surface, it can be performed by shot peening processing or liquid honing processing in which particles are jetted toward the tooth surface. The processing method for injecting particles toward the tooth surface in this way is to change the size of the compressive residual stress, the depth at which the compressive residual stress is maximum, etc., depending on the mass of the particle and the injection speed of the particle. In addition, the strength of the tooth surface, more specifically, the pitting resistance varies depending on the depth at which the compressive residual stress is maximized. For this reason, the depth at which the compressive residual stress is maximized is determined according to the required pitting resistance, and the mass of particles and the injection speed of the particles are determined.

  In addition, shot peening processing and liquid honing processing impart compressive residual stress by spraying particles on the tooth surface as described above. Depending on the amount of energy of the particles, The depth at which the compressive residual stress is maximized changes. Therefore, when the compressive residual stress is large or when the depth at which the compressive residual stress is maximum is deep, the surface roughness of the tooth surface is not small. Therefore, the process which provides a compressive residual stress is performed before grind | polishing a tooth surface.

  In the gear manufacturing method according to the present invention, in the step of applying compressive residual stress, the depth at which the compressive residual stress becomes maximum when the gear is polished and finished is the required target depth. And compressive residual stress. FIG. 1 shows the distribution of compressive residual stress applied to the tooth surface. The solid line indicates the distribution of compressive residual stress before the tooth surface is polished, and the broken line indicates the distribution of compressive residual stress after the tooth surface is polished. Is shown. Note that the horizontal axis in FIG. 1 indicates the depth from the tooth surface, and the vertical axis indicates the magnitude of the compressive residual stress. As shown in FIG. 1, since the maximum value of the compressive residual stress changes to the tooth surface layer side by polishing the tooth surface, in the step of applying the compressive residual stress, the compressive residual stress is increased along with the polishing. It is preferable that the depth at which the compressive residual stress is maximized is increased so that the maximum depth is changed. Specifically, the polishing thickness obtained from the difference between the target surface roughness Rzt and the surface roughness Rza of the rough profile and the target that maximizes the compressive residual stress required to improve the pitting resistance. A shot peening process or a liquid honing process is performed so that the compressive residual stress at the location where the depth is added is maximized. Then, after applying the compressive residual stress, the tooth surface is polished so that the target surface roughness Rzt is obtained. Specifically, the difference between the surface roughness Rza and the target surface roughness Rzt of the rough profile, and the tooth surface are polished.

  The gear manufacturing method described above applies compressive residual stress in consideration of the amount of polishing to reduce the surface roughness of the tooth surface, so that the surface roughness of the polished and finished tooth surface can be reduced. Even if it is polished to reduce its surface roughness, the depth at which the compressive residual stress is maximized is the required target depth, so that the pitting resistance can be improved, that is, the tooth surface. The strength of can be improved. Further, since the target surface roughness Rzt is obtained based on the oil film thickness according to the operating state of the gear, the finished tooth surface can transmit power through the oil film. As a result, power loss during power transmission can be further reduced. Further, the amount of polishing of the tooth surface can be determined from the oil film thickness, and the depth at which the compressive residual stress is maximized can be determined according to the amount of polishing. It is possible to shorten the time required to make a plurality of prototypes of gears with different thicknesses and to find an appropriate depth at which the compressive residual stress is maximized.

Claims (2)

Manufacturing a gear including a step of applying compressive residual stress to tooth surfaces of teeth engaged with each other and a step of reducing the height of the convex portion of the tooth surface to which the compressive residual stress is applied to finish the surface to a predetermined surface roughness. In the method
The height of the convex portion of the tooth surface such that the height of the convex portion of the tooth surface reduced by finishing to the predetermined surface roughness is equal to or less than the oil film thickness interposed between the teeth meshing with each other. Find the amount to reduce
In the step of applying the compressive residual stress, the tooth surface is adjusted to a depth at which the compressive residual stress is maximized to a target depth at which the compressive residual stress in the gear finished to the predetermined surface roughness is maximized. A method for manufacturing a gear, wherein the compressive residual stress is applied as a depth obtained by adding a polishing amount.   The gear manufacturing method according to claim 1, wherein the oil film thickness is obtained based on an average tooth surface speed of the teeth meshing with each other.

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